Field of the Disclosure
This invention relates to a device for detecting infrared radiation, and to a masking section for use with such a detector.
Description of Related Art
Infrared detectors are well known and used in various applications, such as intrusion monitoring. In intrusion monitoring it is known to detect infrared radiation emitted by an intruder using a passive infrared (PIR) detector. Typically a PIR detector includes an infrared detection section and an optical system for directing the infrared radiation from a protected area to the detection section.
Typically, infrared detectors in intrusion detection systems are not able to distinguish accurately between intruders and pets (or other small animals) resulting in undesirable false alarms. To address this problem, the optical system of the infrared detector may be blocked to prevent infrared radiation from detection zones close to the floor from reaching the detection section. Most pets and small animals are expected to remain in these lower detection zones, in contrast to a human intruder that is expected to be detectable in regions higher above the floor.
Some infrared intrusion detection systems increase a threshold for detection. This may be a level which the signal from the infrared detector must exceed before an intruder is considered to be detected, such that a signal due to a pet is insufficient to be considered a detection. This can be achieved electronically in the signal processing from the detector. Some infrared intrusion detection systems distinguish between humans and animals by using algorithms based, for example on input from additional sensors (e.g. video cameras).